Wired Spy Bug

WIRED SPY BUG:

 Circuit Diagram:

Description:

This spy bug circuit will help you to listen to a conversation without being noticed or simply when you want to spy on a person. The circuit is constructed using a Mic, an Amplifier and a Speaker. The device can be wired or wireless depending on the comfort of your design. The device is built around an OpAmp IC741. It consists of a NPN transistor Q1(2N222) and a PNP transistor Q2(2N2907) connected in Push-Pull configuration.

Working:

This circuit can be divided into three sections for better understanding. First part is the Receiver, which is built using an Electric Microphone (Mic) and a Resistor R1. The microphone converts the sound into electrical signal and R1 adjusts the sensitivity of the Mic. The resistor R2 serves as a volume control and capacitor C1 is used to remove the dc component of the signal.

Next comes the pre-amplifier stage which is built using the OpAmp IC741. The IC is wired as an Inverting amplifier and hence the input signal is passed through the inverting terminal of the IC. The positive terminal or the non-inverting terminal is biased using the voltage divider R3 and R4. The resistor R5 is used to provide the negative feedback to the Opamp which in turn controls the gain of the Opamp.

The final stage comes to the amplifier built using the transistors Q1 (2N222) and Q2 (2N2907). These transistors are connected in Push Pull configuration which implies that one of the transistors amplifies the positive half cycle of the input and the other amplifies the negative half cycle. Collectively, we obtain an amplified 180 degree out of phase signal from the amplifier. The signal is then passed through the capacitor C2 to filter out any dc components and then finally to the Speaker.